(1) Field of the Invention
The invention is related in general to wellsite surface equipment such as positive displacement pumps such as fracturing pumps and the like.
(2) Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Hydraulic fracturing of downhole formations typically involves pumping slurry containing suspended proppant, gravel or other solids, at relatively high pressures so as to fracture the rocks. Triplex reciprocating pumps, i.e., a pump having a fluid end with three cylinders, are generally used to pump high pressure fracturing fluids downhole, although other pumps such as quintuplex pumps can also be used.
The pumping cycle of the fluid end cylinders is composed of two stages, a suction cycle and a discharge cycle. In the suction cycle a piston moves outward in a packing bore, thereby lowering the fluid pressure in the fluid end cylinder, opening the suction valve and filling the cylinder with the fluid from a suction pipe, which is sometimes referred to as the suction manifold. In some cases, the pressure is 2-3 times the atmospheric pressure, approximately 0.28 MPa (40 psi). In the discharge cycle, the plunger moves forward in the packing bore, thereby progressively increasing the fluid pressure in the pump, closing the suction valve, opening the discharge valve, and the high pressure fluid flows out of the cylinder into the discharge pipe, and in some cases at 14 to 140 MPa (2 to 20 kpsi).
A positive displacement pump used in high pressure pumping services, such as fracturing and the like, typically require suction stabilization such as pulsation control or the like. The large acceleration head caused by the high volume of fluid between the pump cylinder inlet and the actual stabilizer bladder sometimes are difficult for the stabilizer to overcome. The acceleration head is increased with a higher density fluid, such as fracturing fluid or the like. Many suction stabilizers are mounted disadvantageously external of the suction manifold. Appendage pneumatic or air tank suction stabilizers are known, for example, from WO 02064977 (2002) and U.S. Pat. No. 6,089,837 (2000). Those suction stabilizers mounted on the suction manifold are disadvantageously heavy, are high in cost and require high maintenance.
Suction stabilizers may also be formed from or with a closed cell cellular foam material which have a relatively high gas volume without nitrogen charging. According to the manufacturer, proper sizing and setup is important to performance of the pulsation control equipment, whereas the installed location of the pulsation control equipment is critical, and the recommended location for the pulsation control equipment is within 6 times the nominal pipe diameter of the pump manifold connections. Suction stabilizers are not effective when installed away from the pump. Also, closed cell foams cannot always be utilized with certain materials, such as solvents or the like.
In positive displacement pumps such as fracturing pumps, sand, proppant, or other oilfield materials may build up in the suction manifold at lower pumping rates. Such a buildup may reach a point where the buildup may block the entrance to the pump plunger and cause problems including, but not limited to, cavitations in the cylinder or an introduction of large sand concentration into the pump cylinder causing piston hammer and further physical damage to the pump, the engine, and/or the transmission. While it is known to stabilize the velocity variation of the pump suction feed stream using closed cell foam, these suction stabilizers are not always effective in keeping solids from building up.
It remains desirable to provide improvements in wellsite surface equipment in efficiency, flexibility, reliability, and maintainability.